1. Field of the Invention
This invention relates to an optical disk apparatus capable of recording and reproducing information on an optical disk and, more particularly, to an objective lens actuator capable of driving an objective lens which condenses a laser beam on an optical disk, in each of focusing direction, tracking direction and radial tilt direction.
2. Description of the Related Art
As is well known, recently, the technology of recording information in high density has been developed and optical disks having storage capacity of 4.7 GB (Giga Byte) in one single-sided layer have been widespread. Optical disks such as CD (Compact Disk) and the like are generally known as information storage mediums. Besides the CD, there are DVD (Digital Versatile Disk), HD (High Definition)-DVD, and the like as the optical disks.
When information is recorded on or reproduced from an optical disk, a laser beam is condensed on the recording surface of the disk and an optical beam spot follows information tracks on the optical disk. Moreover, the position and the angle of the objective lens are controlled such that the laser beam is applied to the recording surface of the disk at right angles even if the optical disk is warped.
Control of adjusting the position of the objective lens such that the laser beam is condensed on the recording surface of the disk is called focus control. Control of adjusting the position of the objective lens such that the optical beam spot follows the information tracks on the disk is called tracking control. Control of adjusting the angle of the objective lens such that the laser beam is applied to the recording surface of the disk at right angles is called tilt control. These controls are conducted by employing an objective lens actuator. As the technology of recording the information in high density on the optical disk becomes developed, the objective lens actuator is required to drive the disk in higher accuracy.
Jpn. Pat. Appln. KOKAI Publication No. 2003-257056 discloses a lens actuator using a magnet of bipolar magnetization in which a boundary of magnetization of the magnet is on a diagonal line of a coil.
In the magnetizing pattern disclosed in this document, the Lorentz force applied to the coil is deflected, an undesirable torque is generated and the tilt of the objective lens becomes great when the lens (lens holder) is driven. In addition, in the magnetizing pattern, since the magnitude of the magnetic field generated by the magnet is remarkably fluctuated within the range of movement of the actuator, the sensitivity of driving the actuator is largely varied.